Electronic article surveillance (“EAS”) systems are detection systems that allow the identification of a marker or tag within a given detection zone. EAS systems have many uses, but most often they are used as security systems for preventing shoplifting in stores or removal of property in office buildings. EAS systems come in many different forms and make use of a number of different technologies.
A typical EAS system includes an electronic detection unit, tags and/or markers, and a detacher or deactivator. The detection units can, for example, be formed as pedestal units, buried under floors, mounted on walls, or hung from ceilings. The detection units are usually placed in high traffic areas, such as entrances and exits of stores or office buildings. The tags and/or markers have special characteristics and are specifically designed to be affixed to or embedded in merchandise or other objects sought to be protected. When an active tag passes through a tag detection zone, the EAS system sounds an alarm, a light is activated and/or some other suitable alert devices are activated to indicate the removal of the tag from the prescribed area.
Common EAS systems operate with these same general principles using either transceivers, which each transmit and receive, or a separate transmitter and receiver. Typically the transmitter is placed on one side of the detection zone and the receiver is placed on the opposite side of the detection zone. The transmitter produces a predetermined excitation signal in a tag detection zone. In the case of a retail store, this detection zone is usually formed at an exit. When an EAS tag enters the detection zone, the tag has a characteristic response to the excitation signal, which can be detected. For example, the tag may respond to the signal sent by the transmitter by using a simple semiconductor junction, a tuned circuit composed of an inductor and capacitor, soft magnetic strips or wires, or vibrating magneto acoustic resonators. The receiver subsequently detects this characteristic response. By design, the characteristic response of the tag is distinctive and not likely to be created by natural circumstances.
Radio-frequency identification (“RFID”) systems are also generally known in the art and may be used for a number of applications, such as managing inventory, electronic access control, security systems, and automatic identification of cars on toll roads. An RFID system typically includes an RFID reader and an RFID device. The RFID reader may transmit a radio-frequency (“RF”) carrier signal to the RFID device. The RFID device may respond to the carrier signal with a data signal encoded with information stored by the RFID device.
The market need for combining EAS and RFID functions in the retail environment is rapidly emerging. Many retail stores that now have EAS for shoplifting protection rely on bar code information for inventory control. RFID offers faster and more detailed inventory control over bar coding. Retail stores already pay a considerable amount for hard tags that are re-useable. Adding RFID technology to EAS systems can easily pay for the added cost due to improved productivity in inventory control as well as loss prevention.
In addition, in order to minimize interactions between the EAS and RFID elements, prior art combination approaches have placed the two different elements, i.e., the EAS element and the RFID element, far enough apart in an end-to-end, a side-by-side or a stacked manner so as to minimize the interaction of each element. However, this requires a significant increase in the overall size and footprint of the combination antenna.
Recent attempts to reduce the overall size and footprint of combined EAS and RFID elements and create an antenna having both EAS and RFID capabilities have encountered further difficulties. For example, trying to make EAS and UHF RFID antennas work together in the same space is difficult because the RFID antennas are often designed as a patch antenna that requires a large ground plane.
EAS antennas are often designed as a loop antenna. It is advantageous to place an RFID patch antenna inside the EAS loop antenna. However, problems arise when this is done since the EAS transmit field is significantly attenuated due to the creation of eddy currents in the RFID ground plane which oppose the EAS field. While alternate antenna designs are not subject to the aforementioned problem if the RFID antenna is a dipole or helix coil type antenna, this alternate design does not allow for patch antennas.
What is needed is a combination EAS and RFID antenna design that will allow the placement of the EAS and the RFID elements in close proximity to each other in order to reduce the overall size of the antenna while at the same time reducing the attenuation effects eddy currents.